FREQUENT EXPRESSION OF HUMAN THY-1 ANTIGEN ON PRE-B-CELL ACUTE LYMPHOBLASTIC-LEUKEMIA WITH T(9-22)

Thy-1 (CDw90) is a phosphatidylinositol-anchored protein, and is expre ssed on human pluripotential hematopoietic stem cells. The expression pattern of this antigen on leukemia cells is still controversial. In t his study, 72 adult patients with pre-B cell acute lymphoblastic leuke mia (pre-B ALL) were examined for the expression pattern of Thy-1 by u sing indirect immunofluorescence and reversed transcription polymerase chain reaction (RT-PCR) methods. Twelve cases were judged positive on the basis of conventional immunophenotype criteria. Thirteen cases sh owed a weak clonal shift on the fluorogram, even though their positive percentages were from 6.7% to 14.9%. Thy-1 gene transcripts were dete cted in all of the 13 cases showing a weak clonal shift. The study of antibody binding capacity, which was calculated by the mean fluorescen ce intensity of the test sample on the basis of a calibration curve us ing standard beads, showed that cases with more than 150 sites/cell co uld be positive. Thy-1 positivity in pre-B ALL was not associated with the expression of B-cell differentiation antigens. Thy-1 expression w as significantly higher in pre-B ALL cases with karyotypic abnormaliti es than in those with normal karyotype (p = 0.0071). The t(9;22) abnor mality was found in 18 of the 25 Thy-1(+) cases. Simultaneous expressi on of transcriptional factors, GATA-2 and SCL, was frequently detected in the Thy-1(+) cases. bcr-abl and GATA-2 are thought to play importa nt roles in the proliferation of immature hematopoietic cells. Indeed, cell-cycle analysis showed that the cell population in the S/G2/M pha se of the present Thy-1(+) cases was less than that in the Thy-1(-) ca ses (p = 0.001770). Our data suggest that Thy-1 expression indicates t he proliferative status of the leukemia cells, not their phenotypic im maturity. (C) 1998 Published by Elsevier Science Ireland Ltd. All righ ts reserved.